This worked for me, too. Without knowing the particulars of the .win code, I'm guessing this is some kind of problem on iOS with the old thedonald.win authentication data stored in the browser conflicting with what's trying to be set by authentication.win. I believe that's why deleting data for thedonald.win makes you automatically logged in - whatever is holding things up from the old data is cleared, the data for authentication.win is still there and kicks in to reauthenticate you on thedonald.win.